1. Field of the Invention
The present invention relates to dynamic random access memory ("DRAM") products, and more particularly, to circuitry for programming antifuse elements in DRAM products.
2. Description of the Prior Art
Contemporary DRAM products require a high degree of redundancy in order to improve manufacturing yields. Present redundancy techniques in DRAMs include providing extra memory array columns and/or extra memory array rows which can be used to replace defective columns and/or rows.
Antifuses have been used as nonvolatile programmable memory elements to store logic states which would be used in DRAMs for row and column redundancy implementation. An antifuse is, by definition, a device which functions as an open circuit until programmed to be a permanent short circuit. Antifuses for redundancy implementation are usually constructed in the same manner as the memory cell capacitors in the DRAM array.
Antifuses have other uses in memory products besides redundancy implementation. Antifuses may, for example, be used in integrated circuit memory as a mechanism for changing the operating mode of the memory. Likewise, antifuses may be programmed to encode identification information about the memory, e.g., when the memory was fabricated.
Antifuse elements in DRAM products have typically been programmed by providing a programming voltage to the memory via an external pin which is higher in magnitude than the normal supply voltage V.sub.cc to the memory. Certain problems are, however, created by this approach.
First, the tester that is used to check out the memory product must be capable of providing these higher programming voltages. Second, electrostatic detection (ESD) circuitry on the chip must be modified for the programming voltage, and in doing so, ESD sensitivity may be adversely affected in that the ESD circuits may latch up. The present invention eliminates the need for different ESD structures on a DRAM.